In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The radio access network (RAN) covers a geographical area that is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks may also be called, for example, a “NodeB” (UMTS) or “eNodeB” (LTE). A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Within the local radio area, each cell is identified by an identity, which is broadcast in the cell. The base stations communicate over the air interface with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected, e.g., by landlines or by a microwave link, to a controller node, such as a radio network controller (RNC) or a base station controller (BSC). The controller node supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Terrestrial Radio Access Network (UTRAN) is a third generation mobile communication system, which evolved from the second generation (2G) Global System for Mobile Communications (GSM). UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs). In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity.
3GPP has also developed specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN). E-UTRAN comprises the Long Term Evolution (LTE), which is the radio-access technology, and System Architecture Evolution (SAE), which provides core network functionality. Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected to a core network (via Access Gateways, or AGWs) rather than to radio network controller (RNC) nodes. In general, in LTE the functions of an RNC are distributed between the radio base stations nodes (eNodeB's in LTE) and AGWs. Accordingly, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to RNC nodes. LTE uses Orthogonal Frequency-Division Multiplexing (OFDM) in the downlink and Discrete Fourier Transform (DFT)-spread OFDM in the uplink.
High Speed Downlink Packet Access (HSPA) enhances the WCDMA specification with High Speed Downlink Packet Access (HSDPA) in the downlink and Enhanced Dedicated Channel (E-DCH) in the uplink. HSDPA achieves higher data speeds by shifting some of the radio resource coordination and management responsibilities to the base station from the radio network controller. Those responsibilities include one or more of the following: shared channel transmission, higher order modulation, link adaptation, radio channel dependent scheduling, and hybrid-ARQ with soft combining.
High Speed Downlink Packet Access (HSPA) employs a new transport channel and three new physical channels. The High Speed Downlink Shared Channel (HS-DSCH) is a downlink transport channel shared by several UEs. The HS-DSCH is associated with one downlink DPCH, and one or several physical channels. The following physical channels have been defined for HSDPA: High Speed Physical Downlink Shared Channel (HS-PDSCH); High Speed Dedicated Physical Control Channel (HS-DPCCH); and the High Speed Shared Control Channel (HS-SCCH). The HS-PDSCH is a downlink channel that is both time and code multiplexed. The HS-DPCCH is an uplink channel that carries the acknowledgements of the packet received on HS-PDSCH and also the CQI (Channel Quality Indication). The HS-SCCH is a fixed rate downlink physical channel used to carry downlink signaling related to HS-DSCH transmission. The HS-SCCH provides timing and coding information, thus allowing the UE to listen to the HS-DSCH at the correct time and using the correct codes to allow successful decoding of UE data.
A physical resource of telecommunications technologies such as LTE and High Speed Downlink Packet Access (HSPA) is expressed in terms of a time-frequency grid, where each resource element corresponds to one subcarrier during one symbol interval. In the time domain, LTE downlink transmissions are organized into radio frames, each radio frame consisting of equally-sized subframes.
The International Telecommunications Union-Radio communications sector (ITU-R) has specified a set of requirements for 4G standards, named the International Mobile Telecommunications Advanced (IMT-Advanced) specification. ITU-R has also stated that Mobile WiMAX and LTE, as well as other beyond-3G technologies that do not fulfill the IMT-Advanced requirements, could nevertheless be considered “4G”, provided they represent forerunners to IMT-Advanced compliant versions and have a substantial level of improvement in performance and capabilities with respect to the initial third generation system.
To achieve desired performance requirements of some systems, a concept known as carrier aggregation (CA) has been proposed. With carrier aggregation, two or more component carriers are aggregated for use with a given mobile terminal (“user equipment,” or “UE,” in 3GPP terminology), for supporting high data rate transmissions over a wide bandwidth, while preserving backward compatibility with legacy systems. In carrier aggregation, the user equipment unit (UE) sets up a radio resource control (RRC) connection first. The cell where the RRC connection request is successful becomes the primary cell of the user equipment unit (UE). The carrier frequency where the primary cell belongs is called primary component carrier (PCC). Then, based on UE capability, the network may configure one or more secondary cells (SCC) on other component carriers, which are then called secondary component carriers. These secondary cells are different from the primary cell, for a given UE, and are on different carrier frequencies.
Thus, multi-carrier or carrier aggregation solutions may be used to enhance peak-rates within a technology. For example, it is possible to use multiple 5-MHz carriers in HSPA to enhance the peak-rate within the HSPA network. Similarly, in LTE, multiple 20-MHz carriers or even smaller carriers (e.g., 5-MHz carriers) may be aggregated in the uplink (UL) and/or on the downlink (DL). Each carrier in a multi-carrier or carrier aggregation system is generally termed as a component carrier (CC) or sometimes is also referred to a cell. Simply put, the component carrier (CC) means an individual carrier in a multi-carrier system.
Carrier aggregation (CA) is also sometimes called (e.g., interchangeably called) “multi-carrier system”, “multi-cell operation”, “multi-carrier operation”, “multi-carrier” transmission and/or reception. Carrier aggregation can be used for transmission of signaling and data in the uplink and downlink directions. One of the CCs is the primary component carrier (PCC), which may be referred to as the primary carrier or anchor carrier. The remaining component carriers are called secondary component carrier (SCC) or secondary carriers or even supplementary carriers. Generally, the primary or anchor CC carries the essential UE specific signaling. The primary CC (also known as the PCC or PCell) exists in both uplink and downlink directions in a carrier aggregation deployment. In the event that there is only a single uplink CC, then the PCell is obviously on that CC. The network may assign different primary carriers to different UEs operating in a given sector or cell.
With carrier aggregation, the UE has more than one serving cell in downlink and/or in the uplink: one primary serving cell and one or more secondary serving cells operating on the PCC and SCC(s) respectively. The primary serving cell is interchangeably called as primary cell (PCell) or primary serving cell (PSC). Similarly, the secondary serving cell is interchangeably called a secondary cell (SCell) or secondary serving cell (SSC). Regardless of the terminology, the PCell and SCell(s) enable the UE to receive and/or transmit data. More specifically the PCell and SCell exist in the downlink and uplink for the reception and transmission of data by the UE. The remaining non-serving cells on the PCC and SCC are called neighbor cells.
The CCs belonging to a given carrier aggregation deployment may belong to the same frequency band, in which the deployment may be referred to as using intra-frequency carrier aggregation, or to different frequency bands, in which case the term inter-band carrier aggregation. These may be combined, e.g., where two CCs in band A and 1 CC in band B are used. Inter-band carrier aggregation where two carriers are distributed over two bands is referred to as dual-band-dual-carrier-HSDPA (DB-DC-HSDPA) in HSPA, or simply as inter-band carrier aggregation in LTE. Furthermore the CCs in intra-band carrier aggregation may be adjacent or non-adjacent in frequency domain, the latter approach being referred to as intra-band, non-adjacent carrier aggregation. A hybrid carrier aggregation deployment comprising of intra-band adjacent, intra-band non-adjacent, and inter-band carrier aggregation is also possible.
Using carrier aggregation between carriers of different radio-access technologies (RATs) may be referred to as “multi-RAT carrier aggregation” or “multi-RAT-multi-carrier system” or simply “inter-RAT carrier aggregation”. For example, the carriers from WCDMA and LTE may be aggregated. Another example is the aggregation of LTE and CDMA2000 carriers. Yet another example is the aggregation of LTE FDD and LTE TDD carriers. For the sake of clarity, carrier aggregation within the same technology as described may be regarded as “intra-RAT” or simply “single RAT” carrier aggregation.
Multi-carrier operation may also be used in conjunction with multi-antenna transmission. For example, signals on each CC may be transmitted by the eNB to the UE over two or more antennas.
The CCs in carrier aggregation may or may not be co-located in the same site or base station or radio network node (e.g., relay node, mobile relay node, etc.). For instance, the CCs may originate at different locations, e.g., from non-co-located base stations (BS) or from a BS and a remote radio head (RRH) or remote radio unit (RRU). Examples of combined CA and multi-point communication may include the use of a distributed antenna system (DAS), a remote radio head (RRH), a remote radio unit (RRU), Coordinated multi-point (CoMP) transmission techniques, multi-point transmission/reception techniques, etc. The technology described herein may also apply to any of these and other multi-point carrier aggregation systems.
Depending upon the type of multi-carrier capability and the number of component carriers it supports, a UE may have a single radio-frequency (RF) chain or a plurality of RF chains for multi-carrier operation. For example, a UE may have: (1) a single RF chain for intra-band contiguous carrier aggregation; (2) multiple RF chains for inter-band carrier aggregation; or (3) multiple RF chains for intra-band non-contiguous carrier aggregation.
A multi-carrier SCell setup herein refers to a procedure that enables the network to at least temporarily set up or release the use of a SCell by a carrier-aggregation-capable (CA-capable) UE, in the downlink and/or uplink. The SCell setup or release procedure may comprise: (a) configuration and de-configuration of SCell(s), or (b) activation and deactivation of SCell(s).
A configuration procedure is used by the serving radio network node (e.g., a eNode B in LTE or Node B in HSPA) to configure a CA-capable UE with one or more SCells (a downlink SCell, an uplink SCell, or both). On the other hand, the de-configuration procedure is used by the eNode B to de-configure or remove one or more already configured SCells from a UE's current configuration. The configuration or de-configuration procedure is also used to change a current multi-carrier configuration, e.g., for increasing or decreasing the number of SCells or for swapping the existing SCells with new ones. The configuration and de-configuration are done by the eNode B, in LTE systems, and by the RNC, in HSPA systems, using RRC signaling.
A serving radio network node (e.g., an eNode B in LTE or a Node B in HSPA) may activate one or more deactivated SCells or deactivate one or more SCells on the corresponding configured secondary carriers. The PCell is always activated. The configured SCells are initially deactivated upon addition and after a cell change, e.g., handover. In HSPA the activation and deactivation command is sent by the Node B via HS-SCCH. In LTE the activation and deactivation command is sent by the eNode B via a MAC control element (MAC-CE). The deactivation of SCells saves UE battery power.
A SCell setup or release (i.e., when SCell is configured, de-configured, activated or deactivated) may cause a “glitch,” or an interruption of operation on the PCell or any other activated SCell. Here, “operation” refers to reception and/or transmission on signals. This glitch mainly occurs when the UE has a single radio chain to receive and/or transmit more than one CC. For example, in the case of intra-band carrier aggregation (where CCs are adjacent) the UE may typically have a single radio if the aggregated BW is 40 MHz, e.g., two carriers each of 20 MHz.
The glitch may occur when the CA-capable UE changes its reception and/or transmission bandwidth (BW) from single-carrier to multiple-carrier operation, or vice versa. In order to change the bandwidth the UE has to reconfigure one or more RF components in the RF chain, e.g., an RF filter, a power amplifier, etc. For example, consider a CA-capable UE supporting two DL component carriers, each of 20 MHz: a primary CC (PCC), and one secondary CC (SCC). If the secondary component carrier is deactivated by the serving/primary cell, then the UE will reduce its bandwidth, e.g., from 40 MHz to 20 MHz. This may cause up to 5 milliseconds of interruption on the PCell on PCC, in LTE. Similarly, if the SCell is configured or de-configured, then the PCell may be interrupted, also for up to 5 milliseconds in LTE. In some scenarios or configuration, the interruption may be shorter, e.g., up to 1-2 milliseconds.
The interruption can be caused by any of several factors including RF tuning to reconfigure (i.e., reduce or increase) an RF bandwidth, setting or adjusting of radio parameters such as AGC setting, etc. Examples of scenarios involving shorter interruption times are: when at least two consecutive DL subframes are available, a time-division duplexing (TDD) configuration with more downlink subframes than uplink subframes in a frame is used, etc. In these scenarios, the AGC setting may be done over a shorter time. In HSPA, the interruptions are typically somewhat shorter (e.g., 1 millisecond), since pilot signals are available in all slots in a frame. This in turn leads to a shorter time for adjusting the RF parameters when activating or deactivated SCell. In any case, these interruptions may correspond to the loss of a significant amount of data, especially if the SCell setup or release is performed frequently, e.g., every 20-50 milliseconds.
Setup/release of a downlink SCell may also cause interruptions in the uplink, e.g., when the SCell and PCell (or another SCell) are TDD cells that may have the same or different DL/UL subframe configurations, or even when both SCell and PCell (or another SCell) are frequency-division duplexing (FDD) cells. Similarly, setup/release of an uplink SCell may cause interruptions in the downlink, e.g., when the SCell and PCell (or another SCell) are TDD cells that may have the same or different DL/UL subframe configurations, or even when both SCell and PCell (or another SCell) are FDD cells.
Setup/release of a DL SCell may also, in some cases, cause interruptions for a UE that has multiple RF chains, when the secondary chain is activated/deactivated and tuned. A UE supporting inter-band carrier or intra-band non-contiguous carrier aggregation typically has separate RF chain for each component carrier.
During the interruption period the UE cannot receive from and/or transmit any signal or information to the network. During the interruption the UE may neither perform measurements due to its inability to receive and/or transmit signals.
Bandwidth reduction when SCell is deactivated or de-configured leads to the following benefits from the UE perspective: preventing the UE from receiving noise outside the current reception bandwidth; and saving UE battery life by lowering the power consumption.
A UE-capable UE is required to perform measurements also on the deactivated SCell(s). In the case of a single RF chain (e.g., for intra-band contiguous carrier aggregation), the UE also needs to re-tune the center frequency and the RF bandwidth to obtain a measurement sample for cell search or for neighbor cell measurements (e.g., CPICH RSCP in HSPA, RSRP in LTE, etc.) on a cell belonging to a deactivated SCC. After the measurement sample is obtained, the UE again retunes the center frequency and the RF bandwidth.
Measurements for a serving cell or neighbor cell typically involve a non-coherent averaging of two or more basic non-coherent averaged samples over a measurement period. The details of the sampling depend upon the implementation of a given UE, and are generally not specified by the 3GPP standards. An example of reference symbol received power (RSRP) measurement averaging in E-UTRAN is shown in FIG. 1. FIG. 1 illustrates that the UE obtains the overall measurement quantity result by collecting four non-coherent averaged samples or snapshots, each of 3 milliseconds length in this example, during the physical layer measurement period. The measurement period may be 200 milliseconds when no discontinuous receive (DRX) is used, or when the DRX cycle is not larger than 40 milliseconds. Similar measurement principles apply to UTRAN measurements, such as for Common Pilot Channel (CPICH) Received Signal Code Power (RSCP) measurements.
An interruption occurs before and after each measurement sample, i.e., when the bandwidth is extended (e.g., from 20 MHz to 40 MHz) and also when it is reverted back to the bandwidth of the activated carriers (e.g., from 40 MHz back to 20 MHz). Each of these interruptions may extend over one or two transmission intervals (TTIs), since the UE has to retune the center frequency and the bandwidth of the downlink. This means that an interruption would occur on the PCC before and after each measurement sample. As a consequence the UE can neither transmit on the UL PCC nor receive on the downlink PCC. This is illustrated in FIG. 2. Since the UE must perform measurements also on deactivated SCell(s), data loss on the PCell and activated SCell(s) will also occur whenever the deactivated SCell(s) are measured.
To support different functions such as mobility (e.g., cell selection, cell reselection, handover, RRC re-establishment, connection release with redirection, etc.), minimization of drive tests, self-organizing network (SON), positioning, etc., the UE is required to perform one or more measurements on signals transmitted by neighboring cells. Prior to carrying out such measurements the UE has to identify a cell and determine its physical cell identity (PCI). Therefore PCI determination is also a type of a measurement.
The UE receives measurement configuration or assistance data/information, which is a message or an information element (IE) sent by the network node (e.g., serving eNode B, positioning node, etc.) to configure UE to perform the requested measurements. For example, the measurement configuration may contain information related to the carrier frequency, RATs, type of measurement (e.g., RSRP), higher-layer time-domain filtering, measurement-bandwidth-related parameters, etc.
Measurements are done by the UE on the serving cell as well as on neighbor cells, over some known reference symbols or pilot sequences. The measurements are performed on cells on an intra-frequency carrier, inter-frequency carrier(s) as well as on inter-RAT carriers(s), if the UE is capable of supporting one or more other RATs. The UE may perform measurements on cells belonging to non-serving carriers (i.e., inter-frequency and/or inter-RAT measurements), with or without measurement gaps (e.g., compressed mode gaps in WCDMA/HSPA), depending upon its capability. When performing measurements on cells belonging to non-serving carrier(s) without measurement gaps, the UE may have to retune its receiver bandwidth, e.g., changing the center frequency of its oscillator. This in turn may also cause interruption of signals on the serving cell of the UE. The techniques detailed below are also applicable to this scenario.
In a multi-carrier or carrier aggregation scenario, the UE may perform the measurements on the cells on the primary component carrier (PCC) as well as on the cells on one or more secondary component carriers (SCCs). A CA-capable UE may also perform inter-frequency measurements without measurement gaps, since the UE has a broadband receiver and/or multiple receivers.
Examples of intra-frequency and inter-frequency measurements in LTE are reference symbol received power (RSRP) and reference symbol received quality (RSRQ). Examples of intra-frequency and inter-frequency measurements in HSPA are Common Pilot Channel Received Signal Code Power (CPICH RSCP) and CPICH Ec/No. When the serving cell is HSPA, inter-RAT measurements may include inter-RAT LTE, inter-RAT GSM, inter-RAT CDMA2000, inter-RAT wireless LAN, etc. Examples of GSM measurements are GSM Carrier RS SI. When the serving cell is LTE FDD, the inter-RAT measurements may include inter-RAT LTE TDD, inter-RAT LTE HSPA, inter-RAT GSM, inter-RAT CDMA2000, inter-RAT wireless LAN, etc. When the serving cell is LTE TDD, inter-RAT measurements may include inter-RAT LTE TDD, inter-RAT LTE HSPA, inter-RAT GSM, inter-RAT CDMA2000, inter-RAT wireless LAN, etc.
The mobility measurement may also comprise identifying or detecting a cell, which may belong to LTE, HSPA, CDMA2000, GSM, etc. The cell detection comprises identifying at least the physical cell identity (PCI) and subsequently performing the signal measurement (e.g., RSRP) of the identified cell. The UE may also have to acquire the cell global ID (CGI) of a cell. In HSPA and LTE the serving cell may request the UE to acquire the system information of the target cell. More specifically the SI is read by the UE to acquire the cell global identifier (CGI), which uniquely identifies a cell, of the target cell. The UE also be requested to acquire other information such as CSG indicator, CSG proximity detection, etc. from the target cell.
Examples of positioning measurements in LTE are reference signal time difference (RSTD) for OTDOA positioning and UE RX-TX time difference measurement for E-CID positioning. The UE RX-TX time difference measurement requires the UE to perform measurement on the downlink reference signal as well as on the uplink transmitted signals.
Channel state information (CSI) measurements performed by the UE are used by the network for scheduling, link adaptation, etc. Examples of CSI measurements are channel quality indicator (CQI), precoding channel indicator (PMI), precoding channel indication (PCI), rank indicator (RI), etc. They may be sent periodically or aperiodically by the UE to the network.
The radio measurements performed by the UE are used by the UE for one or more radio operational tasks. Examples of such tasks are reporting the measurements to the network, which in turn may use them for various tasks. For example, in RRC connected state the UE reports radio measurements to the serving node. In response to the reported UE measurements, the serving network node takes certain decisions, e.g., it may send mobility command to the UE for the purpose of cell change. Examples of cell change are handover, RRC connection re-establishment, RRC connection release with redirection, PCell change in carrier aggregation, PCC change in PCC, etc. In idle or low activity state, an example of cell change is cell reselection. In another example, the UE may itself use the radio measurements for performing tasks, e.g., for cell selection, cell reselection, etc.
A HS-PDSCH scheduling allocation is indicated to a UE using the HS-SCCH channel. The scheduling allocation on HS-SCCH is divided into two sections. In the first section (lasting one slot) the number of PDSCH codes, modulation and the number of spatial layers is indicated. The second section (lasting 2 slots) contains further information on transport format, redundancy version, etc., as well as a user specific cyclical redundancy code (CRC). The first section of one slot is transmitter starting two slots prior to the HS-PDSCH transmission.
A UE may also be required to perform inter-frequency or inter-RAT measurements while in CELL_DCH state and being scheduled with HSDPA data. If the UE possesses a single receiver chain and the measurement may be made by means of extending the bandwidth of the receiver chain then the UE may potentially continue to receive data on the PCell whilst making measurements using the wider bandwidth. If the UE possesses two receiver chains, it is possible to use the second receiver chain to tune to another frequency and make measurements whilst receiving data on the first receiver chain. In this manner, the use of compressed mode and interruptions in downlink data reception may be avoided.
If a UE uses its second receiver chain for making measurements (e.g., for SCell measurements, or for inter-carrier or inter-RAT measurements), then the UE needs to activate the chain, adjust the bandwidth and retune to the correct center frequency, make the measurement, and then deactivate the secondary receiver chain (which deactivation may also include a bandwidth change and retuning of the center frequency). The activation and tuning of the chain may cause interference to the primary receiver. If the UE widens the bandwidth of its single receiver chain, it will also cause interference to the reception of signals on the primary receiver and/or on any activated secondary carriers. This momentary interference may interfere with HS-SCCH and HS-DPDSCH or LTE PDSCH reception and in the worst case cause loss of HS-PDSCH or PDSCH TTIs. The loss could be significant in the case of ongoing measurements. The lost data has to be retransmitted leading to delay in reception and increase the load on PCell and/or activated SCell.
Thus, a multi-carrier-capable UE may cause interruption on a serving cell when it retunes its RF receiver or transmitter bandwidth for performing a radio operation related to secondary cell. Examples of such tasks are performing measurements on deactivated SCell, activating or deactivating SCell, configuring or deconfiguring SCell, etc. Alternatively, the UE may adjust the bandwith of its RF receiver in order to perform measurements on cells on any non-serving carrier, e.g., inter-frequency and/or inter RAT measurements. The interruption on serving cell(s) can cause severe performance degradation. It may also be the case that a UE possesses two or more receiver chains and the UE activates its second or additional receiver chain to perform SCell operations or measurements. In some circumstances, activation of a secondary chain may cause a performance glitch or interruption in the reception of signal via primary chain. Accordingly, techniques for mitigating these problems are needed.